The invention claims isolated nucleic acid encoding all or a portion of novel members of the organic anion transport protein (xe2x80x9cOATPxe2x80x9d) designated OATP2, OATP-RP1, OATP-RP2, OATP-RP3, OATP-RP4 and OATP-RP5. Also claimed are vectors containing the nucleic acid sequences, host cells containing the vectors and polypeptides having all or part of the amino acid sequence of OATP2, OATP-RP1, OATP-RP2, OATP-RP3, OATP-RP4 and OATP-RP5. Tissue expression of the transporter is described as well as some of its substrates. Also claimed are uses for these novel OATPs, including for targeting drugs to specific tissues, for modulating the concentration of endogenous substrates, and for identifying a substrate capable of being transported by a novel OATP of the invention.
The liver functions in the clearance of a large variety of metabolic products, drugs and other xenobiotics by transporting them across the sinusoidal membrane into the hepatocyte. Several classes of transport systems have been described that mediate these processes including the Na+/taurocholate cotransporter polypeptide, NTCP, in rat and human liver (Hagenbuch, B., et al. (1991) Proc. Natl. Acad. Sci. USA 88:10629-33; Hagenbuch, B. et al., (1994) J. Clin. Invest. 93:1326-31) and a family of organic anion transporting polypeptides (OATPs) that are principally expressed in liver, kidney and brain, and transport a broad spectrum of substrates in a sodium-independent manner (Meier, P. J., et al., (1997) Hepatology 26:1667-77; Wolkoff, A. W., (1996) Semin. Liver Dis. 16:121-127). The distribution of this latter family of transporters in liver, kidney and choroid plexus in the brain is thought to reflect common physiological requirements of these organs for the clearance of a multitide of organic anions. There are three OATP isoforms in the rat: roatp1 (Jacquemin, E., et al., (1994) Proc. Natl. Acad. Sci. USA 91:133-37); roatp2 (Noe, B. A., et al., (1997) Proc. Natl. Acad. Sci. USA 94:10346-50; and roatp3 (Abe, T., et al., (1998) J. Biol. Chem. 273:11395-401). In addition to bile acids, OATPs are known to transport a variety of other compounds. These include, depending on the transporter, unconjugated and conjugated steroids such as estrone sulfate, estradiol-17B-glucuronide, aldosterone, and cardiac glycosides (Boussuyt, X., et al., (1996) J. Pharmacol. Exp. Ther. 276:891-6; Boussuyt, X. (1996) J. Hepatol. 25:733-8; Kanai, N., et al., (1996) Am. J. Physiol. 270:F319-F325; Kanai, N., et al., (1996) Am. J. Physiol. 270:F326-F331; Noe, B. A., et al., (1997) Proc. Natl. Acad. Sci. USA 94:10346-50). Bromosulfophthalien (Jacquemin, E., et al., (1994) Proc. Natl. Acad. Sci. USA 91:133-7); mycotoxin (Kontaxi, M., et al., (1996) J. Pharmacol. Exp. Ther. 279:1507-13); leukotriene C4 (Li, L., et al., (1 998) J. Biol. Chem. 273:16184-91); and thyroid hormone (Abe, T., et al., (1998) J. Biol. Chem. 273:11395) are additional substrates.
Several proteins have been identified. Jacquemin,E., et al., (1994) Proc. Natl. Acad. Sci. U.S.A., 91:133-137 reported the first cloning and identification of a member of the OATP transporter family, namely the rat oatp1. The first cloning and identification of a human OATP was reported in Kullak-Ublick, G. A., et al., (1995) Gastroenterology, 109:1274-1282. Its expression was found in liver, kidney brain and other organs. The authors concluded, based on substrate specificities, that it was not the human orthologue of rat oatp1.
Substrate specificities of rat oatp1 are discussed in Kullak-Ublick, G. A. et al., (1994) Hepatology, 20:411-416, while substrate specificities of human OATP are discussed in Bossuyt, X., et al., (1996) J. Hepatol., 25:733-738.
Data was later discovered showing that rat oatp1 is involved in the transport of steroids (Bossuyt, X., et al., (1996) J. Pharmacol. Exp. Ther., 276:891-896), and that human OATP acts as a transporter for the psychoactive hormone DHEAS (Kullak-Ublick, G. A., et al., (1998) FEBS Lett., 424:173-176). For a review of the OATP family and organic anoin transport in the liver, see Wolkoff, A. W., (1996) Semin. Liver Dis., 16:121-127.
A third rat OATP isoform that was shown to transport thyroid hormones T3 and T4 was cloned and reported in Abe,T., et al., (1998) J. Biol. Chem., 273:22395-22401.
All references cited herein, whether supra or infra, are hereby incorporated by reference in their entirety.
The present invention encompasses novel organic anion transport proteins (xe2x80x9cOATPxe2x80x9d) and polynucleotides encoding said OATPs. The OATPs disclosed herein are designated OATP2, OATP-RP2, OATP-RP3, OATP-RP4, OATP-RP5 and OATP-RP1. A polynucleotide sequence of each OATP is disclosed herein, along with the deduced amino acid sequence. The cDNAs encoding the OATPs of the present invention have been deposited with the American Type Culture Collection and given Accession Numbers ATCC 207213 (OATP2), ATCC 207212 (OATP-RP2), ATCC 207209 (OATP-RP3), ATCC 207210 (OATP-RP4), ATCC 207211 (OATP-RP5), and ATCC 207214 (OATP-RP1).
The present inventors sequenced the cDNAs encoding the novel OATPs and determined the primary sequence of the deduced proteins. Disclosed herein are the nucleic acid sequence (SEQ ID NO:1) and amino acid sequence (SEQ ID NO:2) of OATP2; the nucleic acid sequence (SEQ ID NO:3) and amino acid sequence (SEQ ID NO:4) of OATP-RP2; the nucleic acid sequence (SEQ ID NO:5) and amino acid sequence (SEQ ID NO:6) of OATP-RP3; the nucleic acid sequence (SEQ ID NO:7) and amino acid sequence (SEQ ID NO:8) of OATP-RP4; the nucleic acid sequence (SEQ ID NO:9) and amino acid sequence (SEQ ID NO:10) of OATP-RP5; and the nucleic acid sequence (SEQ ID NO:11) and amino acid sequence (SEQ ID NO:12) of OATP-RP1.
The OATPs of the present invention can be produced by: (1) inserting the cDNA of a disclosed OATP into an appropriate expression vector; (2) transfecting the expression vector into an appropriate transfection host(s); (3) growing the transfected host(s) in appropriate culture media; and (4) assaying the transport activity in the transfected cells.
The present invention therefore provides a purified and isolated nucleic acid molecule, preferably a DNA molecule, having a sequence which codes for an OATP, or an oligonucleotide fragment of the nucleic acid molecule which is unique to an OATP of the invention. In a preferred embodiment of the invention, the purified and isolated nucleic acid molecule has the sequence as shown in SEQ ID NO:1 (OATP2). In another preferred embodiment, the purified and isolated nucleic acid molecule has the sequence as shown in SEQ ID NO:3 (OATP-RP2). In still another preferred embodiment the purified and isolated nucleic acid molecule has the sequence as shown in SEQ ID NO:5 (OATP-RP3). In still another preferred embodiment of the present invention the purified and isolated nucleic acid molecule has the nucleotide sequence as shown in SEQ ID NO:7 (OATP-RP4). In still another preferred embodiment the purified and isolated nucleic acid molecule has the sequence as shown in SEQ ID NO:9 (OATP-RP5). In still another preferred embodiment of the present invention the purified and isolated nucleic acid molecule has the nucleotide sequence as shown in SEQ ID NO:11 (OATP-RP1).
The invention also contemplates a double stranded nucleic acid molecule comprising a nucleic acid molecule of the invention or an oligonucleotide fragment thereof hydrogen bonded to a complementary nucleotide base sequence.
The terms xe2x80x9cisolated and purified nucleic acidxe2x80x9d, xe2x80x9cisolated and purified polynucleotidexe2x80x9d, xe2x80x9csubstantially pure nucleic acidxe2x80x9d, and xe2x80x9csubstantially pure polynucleotidexe2x80x9d, e.g., substantially pure DNA, refer to a nucleic acid molecule which is one or both of the following: (1) not immediately contiguous with either one or both of the sequences, e.g., coding sequences, with which it is immediately contiguous (i.e., one at the 5xe2x80x2 end and one at the 3  end) in the naturally occurring genome of the organism from which the nucleic acid is derived; or (2) which is substantially free of a nucleic acid sequence with which it occurs in the organism from which the nucleic acid is derived. The term includes, for example, a recombinant DNA which is incorporated into a vector, e.g., into an autonomously replicating plasmid or virus, or into the genomic DNA of a prokaryote or eukaryote, or which exists as a separate molecule (e.g., a cDNA or a genomic DNA fragment produced by PCR or restriction endonuclease treatment) independent of other DNA sequences. Substantially pure or isolated and purified DNA also includes a recombinant DNA which is part of a hybrid gene encoding additional OATP sequence.
The present invention provides in one embodiment: (a) an isolated and purified nucleic acid molecule comprising a sequence encoding all or a portion of a protein having the amino acid sequence as shown in SEQ ID NO:2 (OATP2); (b) nucleic acid sequences complementary to (a); (c) nucleic acid sequences which exhibit at least 80%, more preferably at least 90%, more preferably at least 95%, and most preferably at least 98% sequence identity to (a); or (d) a fragment of (a) or (b) that is at least 18 bases and which will hybridize to (a) or (b) under stringent conditions.
The degree of homology (percent sequence identity) between two sequences may be determined, for example, by comparing the two sequences using computer programs commonly employed for this purpose. One suitable program is the GAP computer program described by Devereux et al., (1984) Nucl. Acids Res. 12:387. The GAP program utilizes the alignment method of Needleman and Wunsch (1970) J. Mol. Biol. 48:433, as revised by Smith and Waterman (1981) Adv. Appl. Math. 2:482. Briefly, the GAP program defines percent identity as the number of aligned symbols (i.e., nucleotides or amino acids) which are identical, divided by the total number of symbols in the shorter of the two sequences.
As used herein the term xe2x80x9cstringent conditionsxe2x80x9d encompasses conditions known in the art under which a nucleotide sequence will hybridize to: (a) an isolated and purified nucleic acid molecule comprising a sequence encoding a protein having the amino acid sequence as shown herein, or to (b) a nucleic acid sequence complementary to (a). Screening polynucleotides under stringent conditions may be carried out according to the method described in Nature, 313:402-404 (1985). Polynucleotide sequences capable of hybridizing under stringent conditions with the polynucleotides of the present invention may be, for example, allelic variants of the disclosed DNA sequences, or may be derived from other sources. General techniques of nucleic acid hybridization are disclosed by Sambrook et al., xe2x80x9cMolecular Cloning: A Laboratory Manualxe2x80x9d, 2nd Ed., Cold Spring Harbor Laboratory, Cold Spring Harbor, N.Y. (1984); and by Haymes et al., xe2x80x9cNucleic Acid Hybridization: A Practical Approachxe2x80x9d, IRL Press, Washington, D.C. (1985), which references are incorporated herein by reference.
The present invention provides in another embodiment: (a) an isolated and purified nucleic acid molecule comprising a sequence encoding all or a portion of a protein having the amino acid sequence as shown in SEQ ID NO:4 (OATP-RP2); (b) nucleic acid sequences complementary to (a); (c) nucleic acid sequences which are at least 80%, more preferably at least 90%, more preferably at least 95%, and most preferably at least 98% sequence identity to (a); or (d) a fragment of (a) or (b) that is at least 18 bases and which will hybridize to (a) or (b) under stringent conditions.
The present invention provides in another embodiment: (a) an isolated and purified nucleic acid molecule comprising a sequence encoding all or a portion of a protein having the amino acid sequence as shown in SEQ ID NO:6 (OATP-RP3); (b) nucleic acid sequences complementary to (a); (c) nucleic acid sequences which are at least 80%, more preferably at least 90%, more preferably at least 95%, and most preferably at least 98% sequence identity to (a); or (d) a fragment of (a) or (b) that is at least 18 bases and which will hybridize to (a) or (b) under stringent conditions.
The present invention provides in another embodiment: (a) an isolated and purified nucleic acid molecule comprising a sequence encoding all or a portion of a protein having the amino acid sequence as shown in SEQ ID NO:8 (OATP-RP4); (b) nucleic acid sequences complementary to (a); (c) nucleic acid sequences which are at least 80%, more preferably at least 90%, more preferably at least 95%, and most preferably at least 98% sequence identity to (a); or (d) a fragment of (a) or (b) that is at least 18 bases and which will hybridize to (a) or (b) under stringent conditions.
The present invention provides in another embodiment: (a) an isolated and purified nucleic acid molecule comprising a sequence encoding all or a portion of a protein having the amino acid sequence as shown in SEQ ID NO:10 (OATP-RP5); (b) nucleic acid sequences complementary to (a); (c) nucleic acid sequences which are at least 80%, more preferably at least 90%, more preferably at least 95%, and most preferably at least 98% sequence identity to (a); or (d) a fragment of (a) or (b) that is at least 18 bases and which will hybridize to (a) or (b) under stringent conditions.
The present invention provides in another embodiment: (a) an isolated and purified nucleic acid molecule comprising a sequence encoding all or a portion of a protein having the amino acid sequence as shown in SEQ ID NO:12 (OATP-RP1); (b) nucleic acid sequences complementary to (a); (c) nucleic acid sequences which are at least 80%, more preferably at least 90%, more preferably at least 95%, and most preferably at least 98% sequence identity to (a); or (d) a fragment of (a) or (b) that is at least 18 bases and which will hybridize to (a) or (b) under stringent conditions.
The present invention also provides: (a) a purified and isolated nucleic acid molecule comprising a sequence as shown in SEQ ID NO:1 (OATP2); (b) nucleic lo acid sequences complementary to (a); (c) nucleic acid sequences having at least 80%, more preferably at least 90%, more preferably at least 95%, and most preferably at least 98% sequence identity to (a); or (d) a fragment of (a) or (b) that is at least 18 bases and which will hybridize to (a) or (b) under stringent conditions.
The present invention further provides: (a) a purified and isolated nucleic acid molecule comprising a sequence as shown in SEQ ID NO:3 (OATP-RP2); (b) nucleic acid sequences complementary to (a); (c) nucleic acid sequences having at least 80%, more preferably at least 90%, more preferably at least 95%, and most preferably at least 98% sequence identity to (a); or (d) a fragment of (a) or (b) that is at least 18 bases and which will hybridize to (a) or (b) under stringent conditions.
The present invention further provides: (a) a purified and isolated nucleic acid molecule comprising a sequence as shown in SEQ ID NO:5 (OATP-RP3); (b) nucleic acid sequences complementary to (a); (c) nucleic acid sequences having at least 80%, more preferably at least 90%, more preferably at least 95%, and most preferably at least 98% sequence identity to (a); or (d) a fragment of (a) or (b) that is at least 18 bases and which will hybridize to (a) or (b) under stringent conditions.
The present invention further provides: (a) a purified and isolated nucleic acid molecule comprising a sequence as shown in SEQ ID NO:7 (OATP-RP4); (b) nucleic acid sequences complementary to (a); (c) nucleic acid sequences having at least 80%, more preferably at least 90%, more preferably at least 95%, and most preferably at least 98% sequence identity to (a); or (d) a fragment of (a) or (b) that is at least 18 bases and which will hybridize to (a) or (b) under stringent conditions.
The present invention further provides: (a) a purified and isolated nucleic acid molecule comprising a sequence as shown in SEQ ID NO:9 (OATP-RP5); (b) nucleic acid sequences complementary to (a); (c) nucleic acid sequences having at least 80%, more preferably at least 90%, more preferably at least 95%, and most preferably at least 98% sequence identity to (a); or (d) a fragment of (a) or (b) that is at least 18 bases and which will hybridize to (a) or (b) under stringent conditions.
The present invention further provides: (a) a purified and isolated nucleic acid molecule comprising a sequence as shown in SEQ ID NO:11 (OATP-RP1); (b) nucleic acid sequences complementary to (a); (c) nucleic acid sequences having at least 80%, more preferably at least 90%, more preferably at least 95%, and most preferably at least 98% sequence identity to (a); or (d) a fragment of (a) or (b) that is at least 18 bases and which will hybridize to (a) or (b) under stringent conditions.
The present invention additionally covers polynucleotides and amino acid sequences of the present invention having one or more structural mutations including replacement, deletion or insertion mutations. For example, a signal peptide may be deleted, or conservative amino acid substitutions may be made to generate a protein that is still biologically competent or active.
The invention further contemplates a recombinant molecule comprising a nucleic acid molecule of the present invention or an oligonucleotide fragment thereof and an expression control sequence operatively linked to the nucleic acid molecule or oligonucleotide fragment. A transformant host cell including a recombinant molecule of the invention is also provided.
In another aspect, the invention features a cell or purified preparation of cells which include a novel gene encoding an OATP of the present invention, or which otherwise misexpresses a gene encoding an OATP of the present invention. The cell preparation can consist of human or non-human cells, e.g., rodent cells, e.g., mouse or rat cells, rabbit cells, non-human primate cells, or pig cells. In preferred embodiments, the cell or cells include an OATP transgene, e.g., a heterologous form of an OATP gene, e.g., a gene derived from humans (in the case of a non-human cell). The OATP transgene can be misexpressed, e.g., overexpressed or underexpressed. In other preferred embodiments, the cell or cells include a gene which misexpresses an endogenous OATP gene, e.g., a gene that expression of which is disrupted, e.g., a knockout. Such cells can serve as a model for studying disorders which are related to mutated or misexpressed OATP alleles for use in drug screening.
Still further, the invention provides plasmids which comprise the nucleic acid molecules of the invention. Also encompassed within the invention are vectors comprising the nucleic acid sequences disclosed herein, as well as host cells comprising said vectors.
The present invention also includes a novel OATP of the present invention, or an active part thereof. A biologically competent or active form of the protein or part thereof is also referred to herein as an xe2x80x9cactive OATP or part thereofxe2x80x9d.
The invention further contemplates antibodies having specificity against an epitope of an OATP of the present invention or part of the protein. These antibodies may be polyclonal or monoclonal. The antibodies may be labeled with a detectable substance and they may be used, for example, to detect a novel OATP of the invention in tissue and cells. Additionally, the antibodies of the present invention, or portions thereof, may be used to make targeted antibodies that destroy OATP expressing cells (e.g., antibody-toxin fusion proteins, or radiolabelled antibodies).
The invention also permits the construction of nucleotide probes which encode part or all of a novel OATP protein of the invention or a part of the protein. Thus, the invention also relates to a probe comprising a nucleotide sequence coding for a protein, which displays the properties of a novel OATP of the invention or a peptide unique to the protein. The probe may be labeled, for example, with a detectable (e.g., radioactive) substance and it may be used to select from a mixture of nucleotide sequences a nucleotide sequence coding for a protein which displays the properties of a novel OATP of the invention.
The present invention also provides a transgenic non-human animal (e.g., a rodent, e.g., a mouse or a rat, a rabbit or a pig) or embryo all of whose germ cells and somatic cells contain a recombinant molecule of the invention, preferably a recombinant molecule comprising a nucleic acid molecule of the present invention encoding an OATP of the invention or part thereof. The recombinant molecule may comprise a nucleic acid sequence encoding an OATP of the present invention with a structural mutation, or may comprise a nucleic acid sequence encoding an OATP of the invention or part thereof and one or more regulatory elements which differ from the regulatory elements that drive expression of the native protein. In another preferred embodiment, the animal has an OATP gene which is misexpressed or not expressed, e.g., a knockout. Such transgenic animals can serve as a model for studying disorders that are related to mutated or misexpressed OATPs of the present invention.
The invention still further provides a method for identifying a substance which is capable of binding a novel OATP of the invention, comprising reacting a novel OATP of the invention or part of the protein under conditions which permit the formation of a complex between the substance and a novel OATP protein or part of the protein, and assaying for substance-OATP complexes, for free substance, for non-complexed OATP, or for activation of an OATP.
An embodiment of the invention provides a method for identifying substrates which are capable of binding to a novel OATP protein of the invention, isoforms thereof, or part of the protein, said method comprising reacting a novel OATP protein of the invention, isoforms thereof, or part of the protein, with at least one substrate which potentially is capable of binding to the protein, isoform, or part of the protein, under conditions which permit the formation of substrate-transporter protein complexes, and assaying for substrate-transporter protein complexes, for free substrate, for non-complexed OATP protein, or for activation of an OATP. In a preferred embodiment of the method, substrates are identified which are capable of binding to and being transported by a novel OATP protein of the invention, isoforms thereof, or part of the protein.
The invention also provides methods for screening potentially useful pharmacological agonists or antagonists of the OATPs of the present invention. The method comprises testing potential agents by adding the agent to be tested to a cell expressing a novel OATP of the present invention in the presence of a compound known to be transported by an OATP of the invention, and measuring the augmentation or inhibition of transport of the known compound.
An OATP of the present invention is also useful to identify compounds that may be transported into an organ, e.g., the liver. Compounds that are found to be actively transported into the liver are useful as carriers for other therapeutics targeting the liver.
Also included within the scope of the present invention is a composition which includes an OATP of the present invention, a fragment thereof (or a nucleic acid encoding said OATP or fragment thereof) and one or more additional components, e.g., a carrier, diluent or solvent. The additional component can be one that renders the composition useful for in vitro, in vivo, pharmaceutical or veterinary use.
Encompassed within the present invention are agonists and antagonists of an OATP of the present invention. Pharmacological agonists or antagonists are useful to increase or decrease the flow of compounds transported by an OATP of the present invention. Said agonists and/or antagonists of the present invention are preferably administered with an acceptable carrier, diluent or solvent.
In another aspect, the present invention relates to a method of treating a mammal, e.g., a human, at risk for a disorder, e.g., a disorder characterized by aberrant or unwanted level or biological activity of an OATP of the present invention. Additionally, encompassed within the invention is a method of treating a mammal, e.g., a human, at risk for disorders of the liver. Since OATP2 is expressed exclusively in the liver, compounds that are optimized for OATP2 are useful to target hepatic delivery. These compounds in themselves may be useful therapeutics, or may be useful to chaperone other therapeutic compounds to the liver. In addition, blocking OATP2-compound interactions could provide benefit by decreasing its first-pass extraction by the liver and, thus, increasing plasma concentrations and prolonging the systemic half-life of a drug.
Also within the scope of the present invention are fusion proteins comprising all or a portion of an OATP of the present invention.
The primary object of the present invention is the identification of new human OATPs, as identified by the nucleic acid and amino acid sequences disclosed herein. Additional objects of the invention are the methods of using the cDNA, the OATP proteins, monoclonal antibodies specific for the novel OATPs, fusion proteins comprising a portion of the OATP protein of the present invention, and agonists and/or antagonists of the novel OATPs as described above.